The present invention relates to a surgical device and more specifically, to a tissue ablation assembly that is adapted to form a conduction block along a length of tissue between two predetermined locations along a left atrial wall.
Cardiac arrhythmia""s, particularly atrial fibrillation, are a pervasive problem in modern society. Although many individuals lead relatively normal lives despite persistent atrial fibrillation, the condition is associated with an increased risk of myocardial ischemia, especially during strenuous activity. Furthermore, persistent atrial fibrillation has been linked to congestive heart failure, stroke, and other thromboembolic events. Thus, atrial fibrillation is a major public health problem.
Normal cardiac rhythm is maintained by a cluster of pacemaker cells, known as the sinoatrial (xe2x80x9cSAxe2x80x9d) node, located within the wall of the right atrium. The SA node undergoes repetitive cycles of membrane depolarization and repolarization, thereby generating a continuous stream of electrical impulses, called xe2x80x9caction potentials.xe2x80x9d These action potentials orchestrate the regular contraction and relaxation of the cardiac muscle cells throughout the heart. Action potentials spread rapidly from cell to cell through both the right and left atria via gap junctions between the cardiac muscle cells. Atrial arrhythmia""s result when electrical impulses originating from sites other than the SA node are conducted through the atrial cardiac tissue.
In most cases, atrial fibrillation results from perpetually wandering reentrant wavelets, which exhibit no consistent localized region(s) of aberrant conduction. Alternatively, atrial fibrillation may be focal in nature, resulting from rapid and repetitive changes in membrane potential originating from isolated centers, or foci, within the atrial cardiac muscle tissue. These foci exhibit centrifugal patterns of electrical activation, and may act as either a trigger of paroxysmal atrial fibrillation or may even sustain the fibrillation. Recent studies have suggested that focal arrhythmia""s often originate from a tissue region along the pulmonary veins of the left atrium, and even more particularly in the superior pulmonary veins.
Several surgical approaches have been developed for the treatment of atrial fibrillation. One particular example, known as the xe2x80x9cmazexe2x80x9d procedure, is disclosed by Cox, JL et al. xe2x80x9cThe surgical treatment of atrial fibrillation. I. Summaryxe2x80x9d, Thoracic and Cardiovascular Surgery 101(3):402-405 (1991) and also by Cox, J L xe2x80x9cThe surgical treatment of atrial fibrillation. IV. Surgical Techniquexe2x80x9d, Thoracic and Cardiovascular Surgery 101(4):584-592 (1991). In general, the maze procedure is designed to relieve atrial arrhythmia by restoring effective SA node control through a prescribed pattern of incisions about the cardiac tissue wall. Although early clinical studies on the maze procedure included surgical incisions in both the right and left atrial chambers, more recent reports suggest that the maze procedure may be effective when performed only in the left atrium (see for example Sueda et al., xe2x80x9cSimple Left Atrial Procedure for Chronic Atrial Fibrillation Associated With Mitral Valve Diseasexe2x80x9d (1996)).
The left atrial maze procedure involves forming vertical incisions from the two superior pulmonary veins and terminating in the region of the mitral valve annulus, traversing the inferior pulmonary veins en route. An additional horizontal incision connects the superior ends of the two vertical incisions. Thus, the atrial wall region bordered by the pulmonary vein ostia is isolated from the other atrial tissue. In this process, the mechanical sectioning of atrial tissue eliminates the atrial arrhythmia by blocking conduction of the aberrant action potentials.
The moderate success observed with the maze procedure and other surgical segmentation procedures have validated the principle that electrically isolating cardiac tissue may successfully prevent atrial arrhythmia""s, particularly atrial fibrillation, resulting from either perpetually wandering reentrant wavelets or focal regions of aberrant conduction. Unfortunately, the highly invasive nature of such procedures may be prohibitive in many cases. Consequently, less invasive catheter-based approaches to treat atrial fibrillation through cardiac tissue ablation have been developed.
These less invasive catheter-based therapies generally involve introducing a catheter within a cardiac chamber, such as in a percutaneous translumenal procedure, wherein an energy sink on the catheter""s distal end portion is positioned at or adjacent to the aberrant conductive tissue. Upon application of energy, the targeted tissue is ablated and rendered non-conductive.
The catheter-based methods can be subdivided into two related categories, based on the etiology of the atrial arrhythmia. First, focal arrhythmia""s have proven amenable to localized ablation techniques, which target the foci of aberrant electrical activity. Accordingly, devices and techniques have been disclosed which use end-electrode catheter designs for ablating focal arrhythmia""s centered in the pulmonary veins, using a point source of energy to ablate the locus of abnormal electrical activity. Such procedures typically employ incremental application of electrical energy to the tissue to form focal lesions. The second category of catheter-based ablation methods are designed for treatment of the more common forms of atrial fibrillation, resulting from perpetually wandering reentrant wavelets. Such arrhythmia""s are generally not amenable to localized ablation techniques, because the excitation waves may circumnavigate a focal lesion. Thus, the second class of catheter-based approaches have generally attempted to mimic the earlier surgical segmentation techniques, such as the maze procedure, wherein continuous linear lesions are required to completely segment the atrial tissue so as to block conduction of the reentrant wave fronts.
An example of an ablation method targeting focal arrhythmia""s originating from a pulmonary vein is disclosed by Haissaguerre et al. in xe2x80x9cRight and Left Atrial Radiofrequency Catheter Therapy of Paroxysmal Atrial Fibrillationxe2x80x9d in Journal of Cardiovascular Electrophysiology 7(12), pp. 1132-1144 (1996). Haissaguerre et al. describe radiofrequency catheter ablation of drug-refractory paroxysmal atrial fibrillation using linear atrial lesions complemented by focal ablation targeted at arrhythmogenic foci in a screened patient population. The site of the arrhythmogenic foci were generally located just inside the superior pulmonary vein, and were ablated using a standard 4 mm tip single ablation electrode.
Another ablation method directed at paroxysmal arrhythmia""s arising from a focal source is disclosed by Jais et al. xe2x80x9cA focal source of atrial fibrillation treated by discrete radiofrequency ablationxe2x80x9d Circulation 95:572-576 (1997). At the site of arrhythmogenic tissue, in both right and left atria, several pulses of a discrete source of radiofrequency energy were applied in order to eliminate the fibrillatory process.
Application of catheter-based ablation techniques for treatment of reentrant wavelet arrhythmia""s demanded development of methods and devices for generating continuous linear lesions, like those employed in the maze procedure. Initially, conventional ablation tip electrodes were adapted for use in xe2x80x9cdrag burnxe2x80x9d procedures to form linear lesions. During the xe2x80x9cdragxe2x80x9d procedure, as energy was being applied, the catheter tip was drawn across the tissue along a predetermined pathway within the heart. Alternatively, lines of ablation were also made by sequentially positioning the distal tip electrode, applying a pulse of energy, and then re-positioning the electrode along a predetermined linear pathway.
Subsequently, conventional catheters were modified to include multiple electrode arrangements. Such catheters typically contained a plurality of ring electrodes circling the catheter at various distances extending proximally from the distal tip of the catheter.
While feasible catheter designs existed for imparting linear ablation tracks, as a practical matter, most of these catheter assemblies have been difficult to position and maintain placement and contact pressure long enough and in a sufficiently precise manner in the beating heart to successfully form segmented linear lesions along a chamber wall. Indeed, many of the aforementioned methods have generally failed to produce closed transmural lesions, thus leaving the opportunity for the reentrant circuits to reappear in the gaps remaining between point or drag ablations. In addition, minimal means have been disclosed in these embodiments for steering the catheters to anatomic sites of interest such as the pulmonary veins. Subsequently, a number of solutions to the problems encountered with precise positioning, maintenance of contact pressure, and catheter steering have been described. These include primarily the use of (1) preshaped ablating configurations, (2) deflectable catheter assemblies, and (3) transcatheter ablation assemblies.
One approach to improved placement has been to use preshaped configurations which impart various predetermined lesion patterns, such as xe2x80x9chairpinsxe2x80x9d or xe2x80x9cJ-shapesxe2x80x9d. Typically, these configurations are situated at the distal end of various steering catheters. Such catheters generally include steering wires, extending from a steering mechanism at the proximal end of the catheter to an anchor point at the distal end of the catheter. By applying tension to the steering wires, the tip of the catheter can be directed in a desired direction. Furthermore, some catheters comprise a rotatable steering feature which allows the catheter as a whole to be rotated about its longitudinal axis, by manipulating the proximal end of the catheter. This exerts a torque which translates to a rotating motion at the distal end which allows a laterally deflected distal tip to be rotated. Once the catheter is steered and positioned to a desired site within an atrial chamber, ablating elements may be activated to form the lesion.
Some preshaped catheter assemblies employ a flexible outer sheath which is advanced over the distal end of the preshaped xe2x80x9cguidexe2x80x9d catheter. Movement of the guide catheter within the sheath modifies the predetermined curve of the distal end of the catheter. By inserting different shaped guide catheters through the outer sheath, different shapes for the distal end of the catheter are created. In one embodiment, the guide catheter position is visualized by X-ray fluoroscopy and progressively repositioned in real time by remote percutaneous manipulation along a preferred pathway in the moving wall of a beating atrium to form continuous lesions.
Deflectable catheter configurations adapted to form curvilinear lesions within an atrial chamber, include devices having a three dimensional basket structure that encloses an open interior at the distal end of the device. The deflectable basket elements may carry single or multiple electrodes. The baskets may be deployed from the catheter by removal of a sheath, done by manipulating the steering assembly located at the proximal end of the catheter. Such deflectable catheter assemblies may form elongated lesions, or simple or complex patterns of curvilinear lesions, depending on the pattern of ablating electrodes on the basket elements. Curvilinear elements may be deployed individually in succession to create the desired maze pattern. In further embodiments, curvilinear elements may include a family of flexible, elongated ablating elements which are controlled by a steering mechanism thereby permitting the physician to create flexes or curves in the ablating elements. Such curvilinear elements include a variety of ablating electrode configurations including linear ribbons and closely wound spirals. A further variation includes the use of gripping members which serve to fix the position of the ablation surface against the atrial wall. The gripping members may include teeth or pins to enhance the ablation of the cardiac tissue by maintaining a substantially constant pressure against the heart tissue to increase the uniformity of the ablation.
Transcatheter-based assemblies include systems for creating both linear lesions of variable length or complex lesion patterns. Such assemblies and methods involve catheter systems which can adapt to the tissue structures and maintain adequate contact and which are easily deployable and maneuverable. One example of a transcatheter-based assembly and method for creating complex lesion patterns includes the use of flexible electrode segments with an adjustable coil length which may form a convoluted lesion pattern of varying length. This device includes a composite structure which may be flexed along its length to form a variety of curvilinear shapes from a generally linear shape.
Other transcatheter ablation assemblies include the use of steerable vascular catheters which are expanded to conform to the surface of the cardiac chamber. One such expandable system comprises single or multiple proximally constrained diverging splines which expand upon emergence from the distal end of a catheter sheath, like the deflectable basket assembly described above. The splines are sufficiently rigid to maintain a predisposed shape but are adapted to be deflected by contact with the cardiac chamber wall. This expandable multi-electrode catheter is adapted to be positioned against the inner wall of a cardiac chamber to create linear continuous lesions.
Another example describes an expandable structure and method for ablating cardiac tissue, including a bendable probe which is deployed within the heart. The probe carries at least one elongated flexible ablation element, a movable spline leg and further including a bendable stylet in a single loop support structure. The assembly provides for tension to bend the stylet which then flexes the ablation element into a curvilinear shape or other readily controlled arcuate catheter shapes to allow a close degree of contact between the electrode elements and the target tissue for forming long, thin lesion patterns in cardiac tissue.
An additional example of a bendable transcatheter assembly comprises an outer delivery sheath and an elongated EP device slideably disposed within the inner lumen of the delivery sheath and secured at its distal end within the delivery sheath. The EP device has a plurality of electrodes on its distal portion. Proximal manipulation of the EP element causes the distal portion of the EP device to arch, or xe2x80x9cbowxe2x80x9d outwardly away from the distal section of the delivery sheath which engages the heart chamber, thereby forming a linear lesion in atrial wall.
None of the present catheter-based devices, however, include a tissue ablation assembly having two separate and independent delivery members with an elongated ablation member coupled therebetween. Nor does the prior art disclose an assembly where the ablation member is adapted to variably extend from a passageway through a distal port in one of the delivery members, thereby providing an ablation means having an adjustable length, extending between the first and second delivery members. Nor does the prior art disclose a method for securing the ablation member between a first and second anchor, thereby maintaining a desired linear position in contact with the atrial wall and facilitating the formation of a linear ablation track along the length of tissue between the anchors.
A tissue ablation device assembly is provided which is adapted to form a conduction block along a length of tissue between first and second predetermined locations along an atrial wall of an atrium in a patient.
According to one mode of the assembly, a first delivery member has a proximal end portion and a distal end portion with a first anchor, a second delivery member has a proximal end portion and a distal end portion with a second anchor, and an ablation member has first and second end portions and an ablation element between those end portions. The ablation member""s end portions are engaged to the distal end portions of the first and second delivery members, respectively. In addition, the first and second anchors are adapted to secure the ablation element to the first and second predetermined locations in order to secure the ablation element along the length of tissue.
According to another mode of the assembly, first and second delivery members each have proximal and distal end portions, and an ablation member has first and second end portions with an ablation element between those end portions. The proximal end portions of the first and second delivery members are adapted to slideably engage a delivery sheath in a side-by-side arrangement. By manipulating the proximal end portion of the first delivery member externally of the body, the distal end portion of the first delivery member is adapted to controllably position the first end portion of the ablation member within the atrium and to secure the ablation element to the first predetermined location. Similarly, by manipulating the proximal end portion of the second delivery member externally of the body, the distal end portion of the second delivery member is adapted to controllably position the second end portion of the ablation member within the atrium and to secure the ablation element to the second predetermined location.
According to another mode of the assembly, a first delivery member has proximal and distal end portions and a passageway that extends between a distal port located along the distal end portion and a proximal port located proximally of the distal port. A second delivery member is also provided having proximal and distal end portions. An ablation member has a first end portion that is slideably engaged with an adjustable position within the passageway in the first delivery member, a second end portion that is engaged to the distal end portion of the second delivery member, and an ablation element with an ablation length located between the first and second end portions. Further to this mode, at least a portion of the ablation member which includes the ablation element is adapted to extend distally from the passageway through the distal port with an adjustable length extending between the first and second delivery members.
According to a further mode of the assembly, a first delivery member has a proximal end portion, a distal end portion with a first anchor, and a passageway that extends between a distal port located along the distal end portion and a proximal port located proximally of the distal port. An ablation member has a first end portion that is slideably engaged within the passageway with an adjustable position, and also has a second end portion which includes the ablation element that is adapted to extend distally from the passageway through the distal port with an adjustable length. The adjustable length between the distal port in the first delivery member and the second end portion of the ablation member is achieved by slideably adjusting the position of the first end portion of the ablation member within the passageway. Further to this mode, a second anchor is also located along the second end portion of the ablation member. The first and second anchors of this assembly are adapted to secure the ablation element to the first and second predetermined locations, respectively, such that at least a portion of the ablation length is secured to and extends along the length of tissue.
In one further aspect of the modes just described, a tracking member for tracking over a guidewire or other guidemember is included with the first or second delivery member, or the first or second anchor. Alternatively, a guidewire tracking member may be provided for each of two of these assembly components, thereby adapting the assembly to track over two wires in order to string the ablation element between adjacent vessels respectively engaged by those wires. Further to this aspect, one or more guidewire tracking members has a passageway for tracking over a guidewire and which terminates in a distal port. Accordingly, the ablation member may be engaged to the guidewire tracking member either at or adjacent to the distal port or proximally thereof.
In another aspect of the modes just described, first and second actuating members are positioned within the first and second delivery members. Each actuating member terminates proximally at a proximal coupler along the proximal end portion of the respectively engaged delivery member, the proximal couplers being adapted to couple to an ablation actuator. In one variation of this aspect, the ablation element is an electrode element with one or more electrodes and each ablation actuating member is an electrical lead wire. In another variation, the ablation element includes an ultrasound transducer and each ablation actuating member is an electrical lead which is coupled to a different surface on that transducer.